Observations on rabbit blastocysts prepared as flat mounts.

T H E structure of the mammalian blastocyst has generally been studied on whole mounts in fluid, or on sections of embedded preparations. If the blastocyst of the rabbit is split open and mounted flat, however, the intact cells in their correct topographical relationships may be examined under the high powers of the microscope. This technique, which is quick and simple, may be employed in cytological and cytochemical studies of the large blastocyst cells, in study of mitotic patterns in the blastocyst wall, and in evaluation of the effects of culture media and of various experimental techniques applied to the blastocysts themselves or to the mother.